Gastroesophageal reflux occurs when stomach acid intermittently surges into the esophagus. It is common for most people to experience this acid reflux occasionally as heart burn. Gastroesophageal reflux disease (GERD) is a clinical condition in which the reflux of stomach acid into the esophagus is frequent enough and severe enough to impact a patient""s normal functioning or to cause damage to the esophagus. GERD is sometimes also referred to as xe2x80x9crefluxxe2x80x9d or xe2x80x9creflux esophagitis.xe2x80x9d
It has been estimated by the U.S. Department of Health and Human Services that about seven million people in the United States suffer from GERD. The incidence of GERD increases after the age of 40, and more than 50 percent of those afflicted with GERD are between the ages of 45-64. (Statistics from Digestive Diseases in the United States: Epidemiology and Impact, National Digestive Diseases Data Working Group, James E. Everhart, MD, MPH, Editor, U.S. Department of Health and Human Services, Public Health Service, National Institutes of Health, NIH Publication No. 94-1447, May 1994.) For general information about GERD see the following: Fennerty, M. B., Sampliner, R. E., Gastroesophageal reflux disease, Hospital Medicine, 29(4): 28-40 (1993); and Orlando, R. C., Reflux esophagitis, in Textbook of Gastroenterology, 1: 1123-1147, Yamada, T., ed., J. B. Lippincott Co., Philadelphia, Pa. (1991).
In the lower part of esophagus, where the esophagus meets the stomach, there is a muscular valve called the lower esophageal sphincter (LES). Normally, the LES relaxes to allow food to enter into the stomach from the esophagus. The LES then contracts to prevent stomach acids from entering the esophagus. In GERD, the LES relaxes too frequently or at inappropriate times allowing stomach acids to reflux into the esophagus.
The most common symptom of GERD is heartburn. Acid reflux also leads to esophageal inflammation, which causes symptoms such as odynophagia, or painful swallowing, and dysphagia, or difficulty swallowing. Pulmonary symptoms such as coughing, wheezing, asthma, or inflammation of the vocal cords or throat may occur in some patients. More serious complications from GERD include esophageal ulcers and esophageal stricture, or narrowing of the esophagus. The most serious complication from chronic GERD is a condition called Barrett""s esophagus in which the epithelium of the esophagus is replaced with abnormal tissue. Barrett""s esophagus is a risk factor for the development of cancer of the esophagus.
Accurate diagnosis of GERD is difficult but important. Accurate diagnosis allows identification of individuals at high risk for developing the complications associated with GERD. It is also important to be able to differentiate between gastroesophageal reflux, other gastrointestinal conditions, and various cardiac conditions. For example, the similarity between the symptoms of a heart attack and heart burn often lead to confusion about the cause of the symptoms.
Several methods are currently being used to diagnose GERD and its associated complications. In healthy subjects, esophageal pH values are greater than pH 4 most of the time, and are lower than pH 4 only a very small percentage of the time. Therefore, an esophageal pH of less than pH 4 is generally used as the threshold to determine the presence of excessive acid reflux. See, e.g. H. G. Dammann, M.D., University of Hamburg, Hamburg Science Institute for Clinical Research xe2x80x9cThe Relevance of Acidity Measurements in the Management of Gastro-oesophageal Reflux Disease,xe2x80x9d Research and Clinical Forums, 20(2):19-26 (1998) (healthy subjects had an esophageal pH of less than pH 4 approximately 1.5% of the time within a twenty-four hour period); and Jamieson J. R., Stein H. J., DeMeester T. R., Bonavina L., Schwizer W., Hinder R. A., and Albertucci M., xe2x80x9cAmbulatory 24-hour esophageal pH monitoring: normal values, optimal thresholds, specificity, sensitivity, and reproducibility,xe2x80x9d Am. J. Gastroenterol., 87(9):1102-11 (1992).
It is difficult to accurately test esophageal pH because the episodes of acid reflux into the esophagus are sporadic even in patients with severe reflux disease. Within a twenty-four hour period, the episodes of reflux may only occur about 10 to 15 percent of the time. See, e.g. Fink, S. M., and McCallum, R. W., xe2x80x9cThe role of prolonged esophageal pH monitoring in the diagnosis of gastroesophageal reflux,xe2x80x9d JAMA, 252(9):1160-64 (1984) (during 24-hour pH monitoring, the mean percentage time that pH was less than pH 4.0 was approximately 13.2% for GERD patients, and approximately 2.9% for normal subjects); and Vitale, G. C. et al., xe2x80x9cComputerized 24-hour ambulatory esophageal pH monitoring and esophagogastroduodenoscopy in the reflux patient: a comparative study,xe2x80x9d Ann. Surg., 200(6):724-728 (1984) (the mean length of time of reflux below pH 4 was 5.41 minutes/hour, or approximately 9 percent of the time, in patients with reflux symptoms, and 0.70 minutes/hour, or approximately 1.2 percent of the time, in normal subjects). At any given time, the esophageal pH is likely to be normal. Therefore, it is important to assess the total time during which the esophagus is exposed to a clinically significant low pH over an extended period of time, such as twenty-four hours.
These studies indicate that in patients who exhibit symptoms of reflux, the percentage of time during which the esophageal pH is less than pH 4 may vary, and may be in the range of only ten to fifteen percent of the time. In normal subjects, esophageal pH is less than pH 4 only a very small percentage of the time, typically between one to three percent of the time. Therefore, an esophageal pH of less than about pH 4 for about five or more percent of the time is indicative of the symptoms of reflux. The percentage of time during which the patient""s esophagus is exposed to pH levels less than about pH 4 is correlated with the severity of the diseasexe2x80x94the greater the time of exposure, the more severe the condition. An esophageal pH of less than about pH 4 for about ten or fifteen percent of the time is indicative of more severe GERD.
Esophageal manometry, esophageal endoscopy, and esophageal pH monitoring are standard methods of measuring esophageal exposure to stomach acids and are currently used to diagnose GERD. Conventional pH monitoring involves placing a pH probe in the esophagus. Preferably, esophageal pH monitoring would take place over a twenty-four hour period.
Several methods of gastrointestinal pH monitoring have been used including intubation methods, ingestible capsules, glass electrodes, and radiotelemetry pills. Intubation involves the insertion of a tube into the patient. The tube is inserted through the nose and into the gastrointestinal tract of the patient. There may be a device at the inserted end of the tube which allows retrieval of a sample for further analysis, as disclosed in U.S. Pat. No. 4,735,214. Alternatively, the tube may be associated with an acid-base indicator, as disclosed in U.S. Pat. No. 3,373,735. Intubation methods are generally used for pH monitoring at a specific time, which does not allow for a determination of time exposure to clinically significant low pH. Intubation is also painful and uncomfortable, and it must be carried out in a hospital or clinical setting.
Tubeless methods and ingestible capsules have also been used to measure gastrointestinal pH. Ingestible capsules have been used to determine pH levels at a specific time and to retrieve samples from the gastrointestinal tract of a patient for further analysis. An ingestible capsule using an ion-exchange color indicator has also been suggested for use in twenty-four hour monitoring of esophageal pH, as disclosed in U.S. Pat. No. 4,632,119.
Electronic pH monitoring devices have also been used. A glass electrode or a radiotelemetry pill is introduced nasally or orally and is positioned in the esophagus proximal to the LES. The pH probe is connected to a microprocessing unit and pH levels are continuously recorded over a twenty-four hour period. (See, Colson, et al., xe2x80x9cAn Accurate, Long-Term, pH-Sensitive Radio Pill for Ingestion and Implantation,xe2x80x9d Biotelemetry Patient Monitg., 8: 213-227 (1981). This type of monitoring may take place in a hospital or clinic. Alternatively, with a portable microprocessor, the patient may be ambulatory. Even with a portable unit, the procedure is uncomfortable, and the apparatus is cumbersome. The probe is passed through the nose, and wires extending from the probe course over the face, across the chest, and attach to a recording device worn on a belt. Both the appearance of the apparatus and the discomfort it causes may restrict a patient from engaging in his normal daily activities, thus interfering with the diagnostic result. Additionally, electronic pH monitoring is expensive and requires computer analysis of the data gathered.
In one aspect, the present invention provides methods and apparatus for a gastrointestinal pH monitor utilizing an ingestible and retrievable radioactive capsule swallowed and held in the esophagus by means of a cord. Presence of acid in the esophagus causes pH-dependent degradation of the capsule and a decrease in the amount of radioactivity in the capsule. The capsule is assayed before and after placement in the esophagus and the residual radioactivity is correlated with overall acid exposure over a given period of time.
In another aspect, the present invention provides methods and apparatus for an ambulatory gastrointestinal diagnostic device which provides a semiquantitative determination of the duration of esophageal exposure to pH levels clinically significant for gastroesophageal reflux disease.
In another aspect, the present invention provides methods and apparatus for a gastrointestinal diagnostic device that is inexpensive, comfortable, and easy to use and does not interfere with a patients normal daily activities, allowing accurate twenty-four hour analysis of the patient""s gastrointestinal tract.
In another aspect, the present invention provides methods and apparatus for diagnosing gastroesophageal reflux disease.